Liquid phase epitaxy of AlxGa1−xP on GaP and its application to double heterostructure light modulators

Single- and double-heterojunction structures of Al_xGa_1?xP/GaP were grown by liquid phase epitaxy and their opto-electronic properties were characterized. Using a starting growth temperature of 900°C, a background impurity level in undoped Al_0.5Ga_0.5P of 1 × 10¹⁶ cm^-3 (p-type) is obtained. The growth rate of Al_xGa_1?xP was very low. An almost intrinsic layer exists at the p-n Al_xGa_1?xP/GaP heterojunction interface due to the interdiffusion of the dopants. By using a rotating slide liquid phase epitaxial growth technique, we have made a high efficiency light modulator from a Al_xGa_1?xP/GaP double heterostructure. The employment of a dummy crystal resulted in very good reproducibility of the GaP waveguide layer thickness. Light is well confined in the GaP layer and a voltage difference, V_π, of 6 V is enough to obtain the phase difference, π, between TE and TM modes.     

Growth of bubble-free Ti-doped Al2O3 single crystal by the czochralski method

The behaviour of bubble entrapment in Ti-doped Al₂O₃ single crystals grown by the Czochralski method was studied from the view point of crystal growth conditions such as the crystal rotation rate and kinds of growth atmosphere. The entrapment of bubbles was not correlated with the shape of solid-liquid interface dependent on crystal rotation rate. We found that the use fo He atmosphere, instead of the conventional atmosphere such as Ar, suppresses the formation of bubbles.     

On the Solubility of Garnets in PbO/B2O3 High Temperature Solvents

The paper is concerned with solubility models for Y₃Fe₅O₁₂ (YIG) and Gd₃Ga₅O₁₂ (GGG) solved in PbO/B₂O₃ high temperature solutions containing Fe₂O₃ or Ga₂O₃ in excess. It is shown that a new extended eight-particle model Interprets well the literature data of the solubility of YIG as well as the DTA data of the solubility of GGG. Comparisons of solution enthalpies determined in terms of the single-molecule, eight-particle, and extended eight-particle model are carried out in dependence on the excess concentration of species containing iron or gallium, respectively.     

Dipeptide-assisted growth of uniform gallium oxohydroxide spindles

The catalytic dipeptide His–Ser was used as an additive in mineralizing gallium ions to form GaOOH, a solid precursor of Ga₂O₃. This dipeptide was chosen to mimic the enzyme structure of silicatein, similar to the well-known catalytic triad of chymotrypsin. The dipeptide promoted formation of spindle-structured GaOOH under acidic conditions by behaving as a heterogeneous nucleation seed. In contrast, no well-defined, structured gallium species were produced in the absence of dipeptide. The catalytic function of the dipeptide was most pronounced at pH values in the range 3–5, which are lower than the pKa of imidazole in the His side chain. These results suggest that the catalytic role of dipeptide influences the gallium hydroxide conversion and growth. This study suggests that a designed peptide with active functionality can be further exploited to produce inorganic compounds with controlled nucleation and growth.     

Das quaternäre Schmelzdiagramm Ga?As-P Sn

The pseudoternary cut Sn GaAs GaP of the quarternary system Ga As P Sn has been investigated in a temperature range from 860 to 1200°C. The calculation based on Vieland's method by use of Darken's quadratic formalism. A comparision between the solvents tin and gallium shows a higher solubility in tin for the mixed crystal Ga_xPAs_1−x and a stronger variation of the composition along the growth direction.     

Study on the possibility of native oxide removal from GaP and GaAs surface by etching,using model experiments

Crystallites of α-Ga₂O₃, β-Ga₂O₃, GaOOH, GaPO₄ and an amorphous phase have been detected previously on chemically etched GaP- and GaAs surfaces. The same compounds were prepared separately and submitted to solubility study, applying several etchants used in etching practice. It could be observed that the solubility of gallium oxides decreases as the chemically bound water is diminished, the anhydrous β-Ga₂O₃ being almost insoluble. As the same poorly soluble oxide forms were found on etched GaP and GaAs surfaces, the difficulties occurring in etching practice can be connected with their presence.     

Experimental study of bubble generation during β‐BaB2O4 single crystal growth

The generation of bubble‐inclusions during BaB₂O₄ (BBO) crystal growth from high temperature solution has been optically observed by an in situ observation technique. It was found that bubbles are formed from the peripheries of some hexagonal defects in the (0001) plane of the growing crystal, which may be caused by the evaporation of the air‐opened interface at the high temperature. In addition, atomic force microscope (AFM) was used to investigate the distribution of bubbles. Results revealed that the bubble generation and distribution depend strongly on the microscopic structure of the interface: on a rough interface, bubbles are easily formed and grow rapidly; however, they are greatly suppressed by step trains on a vicinal interface. In the latter case, the height value of a bubble is close to that of the step, which is in the order of several tens of nanometers. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical properties of Sr3TaGa3Si2O14 single crystal

The specific rotation ρ of strontium tantalum gallium silicate Sr₃TaGa₃Si₂O₁₄ (STGS) piezoelectric single crystal was determined from 350 to 850 nm by measuring the optical transmission between parallel polarisers in Z direction. It is shown that Sr₃TaGa₃Si₂O₁₄ has quite large a value of ρ which is a little smaller than that of strontium niobium gallium silicate Sr₃NbGa₃Si₂O₁₄ (SNGS). The crystal with ordered structure which is isostructural to calcium gallium germanate Ca₃Ga₂Ge₄O₁₄ (CGG) was grown by Czochraiski technique. And its birefringence was also determined. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of the nature of point defects in in Te-doped gallium antimonide

Precision lattice constant and density measurements held on gallium antimonide single crystals grown from stoichiometric melts showed that doping of such crystals with Te lead to the intensification of Ga-supersaturated solid solution decomposition process with initial Frenkel defect (Ga_i + V_Ga) production. It is supposed that Te_sb — simple donors form complexes with V_Ga which are believed to be acceptors. Doping of GaSb with Te up to the levels above 2 · 10¹⁸ cm⁻³ leads to partial decomposition of GaSb(Te) solid solution supersaturated with Te.     

Characterization of SHG candidate crystals in barium aluminum (gallium) borates

Crystals listed in the JCPDS card in BaO‐B₂O₃‐Al₂O₃ and BaO‐B₂O₃‐Ga₂O₃ systems were synthesized by means of a solid‐state reaction method and a liquid‐state reaction method. Synthesized crystals were characterized from a viewpoint of Second Harmonic Generation (SHG) and crystal growth possibility. Ba₅Al₄B₁₂O₂₉ and Ba₅Ga₄B₁₂O₂₉ are promising new candidate crystals from the viewpoint of SHG activity and congruent melting behavior. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Gas bubble associated mass transport in Bridgman-Stockbarger melt growth system

Experimental evidence has been obtained showing that gas bubbles may be responsible for melt stirring in Bridgman-Stockbarger growth system which results in Pfann type impurity distribution profiles along the crystal length. The hypothesis of the gas bubble associated mass transfer mechanism is supported by the production of Y₃Al₅O₁₂–Nd³⁺ single crystals under conditions which eliminate or limit gas bubble nucleation in the melts with Nd³⁺ distribution profiles similar to those generally observed in melt growth systems where the mass transport in the melts is limited to diffusion.     

Glass formation and properties in the gallia-calcia system

The critical cooling rate for glass formation was measured for five compositions in the Ga₂O₃?CaO system and varied from a low of (315 ± 85) °C/s for a eutectic melt containing 37.5 mol.% Ga₂O₃ to a high of (840±60)°C/sec for a melt containing 52 mol.% Ga₂O₃. Selected properties of glasses containing from 37.5 to 62 mol.% Ga₂O₃ were measured. The density and refractive index, n_D, both increased with increasing Ga₂O₃ content, but the crysallization temperature and microhardness varied only slightly with Ga₂O₃ content. The IR spectra of these glasses suggest that both GaO₄ tetrahedra and GaO₆ octahedra are present.     

Single‐crystal growth and characterization of mullite‐type orthorhombic Bi2M4O9 (M = Al3+, Ga3+, Fe3+)

Pure and homogeneous single crystals of orthorhombic mullite‐type Bi₂M₄O₉ (M = Al³⁺, Ga³⁺, Fe³⁺), and a mixed Bi₂Fe_1.7Ga_2.3O₉ crystal from an equimolar Ga/Fe composition were grown by the top seeded solution growth (TSSG) method. All these compounds melt incongruently in the range of about 800 and 1100 °C. In case of bismuth gallate and ferrate inclusion‐free crystals with dimensions up to several cubic centimeters can be grown. Limited solubility in Bi₂O₃ and the high steepness of the liquidus curve are the reasons for getting only small imperfect bismuth aluminate crystals. In contrast to ceramic materials preparation reported in literature, divalent calcium and strontium could not be incorporated into the mullite‐type structure during the melt growth process. Several fundamental physical properties like heat capacity, thermal expansion, heat conductivity, elastic constants, high‐pressure behavior and oxygen diffusivity were determined by different research groups using single‐crystalline samples from the as‐grown materials. Furthermore, the refractive indices of Bi₂Ga₄O₉ were measured in the range of 0.430 and 0.700 μm. Such as many other bismuth containing compounds the refractive indices of Bi₂Ga₄O₉ are larger than 2, and Bi₂Ga₄O₉ is an optic biaxial positive crystal. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of GaN crystal by the reaction of Ga with Li3N in NH3 atmosphere

A novel method to synthesize GaN crystals was studied by the reaction of Ga with Li₃N under NH₃ atmosphere. We have already reported the synthesis technique of GaN by the reaction of Ga₂O₃ with Li₃N. However, the size of GaN crystals obtained by this method was limited to be smaller than several micrometers because of the solid phase reaction. In order to increase the size of GaN crystals, the method using liquid Ga as gallium source was studied for solid–liquid phase reaction. We found that the GaN crystals with the size of more than 100 μm were synthesized at 750 °C for 24 h under NH₃ atmosphere. We propose the possible reaction mechanism as follows. Lithium amide (LiNH₂) is synthesized by the reaction of Li₃N with NH₃ gas and then the crystal growth of GaN occurs by the reaction of Ga with LiNH₂. We found that LiNH₂ is a useful nitrogen source for the GaN synthesis method.     

LPE growth of YLaTm and YLaEu garnet films

The growth of films of the composition Y_3?(x+yLa_xR_yFe_5?zGa_zO₁₂, where R = Tm or Eu, on GGG substrates by liquid phase epitaxy from a PbO-B₂O₃ fluxed melt is described. Highly uniform, low defect density films have been grown by means of horizontal dipping using intermittent substrate rotation in conjunction with a novel substrate holder. A furnace with three separate temperature zones was used to optimize the vertical temperature profile. Incorporation of La into the films allows compositions containing Tm to be made whose lattice parameters are matched to GGG and compositions which contain Eu to be made with smaller Eu concentrations than were previously possible. The compositions grown, which contain only trivalent cations, exhibit growth induced anisotropy, high mobility, low coercivity, and sufficient magnetostriction to allow ion implantation to effectively suppress hard bubble formation. Detailed measurements of saturation temperature as a function of oxide concentration show that the La ion contributes differently to the garnet phase than do other commonly used rare earth cations. The kinetics of melt equilibration have been studied and procedures to equilibrate the melt to ensure reproducible film growth are described. Electron microprobe analysis has been used to determine the La distribution coefficient as a function of La concentration, the growth rate of the film, and the melt temperature.     

Effect of Starting Melt Composition on Crystal Growth of La3Nb0.5Ga5.5O14

Single crystals of La₃Nb_0.5Ga_5.5O₁₄ were grown from different starting melt compositions by the Czochralski technique. The effect of the melt composition on crystal quality was examined by measuring the variation of chemical composition and lattice parameters along the growth axis. The existence of a solid solution range of La₃Nb_0.5Ga_5.5O₁₄ is discussed using X-ray crystal structure analysis.     

Bubble transport in three-dimensional laminar gravity-driven flow - numerical results

This paper is the second part of a study on bubble transport, growth and shrinkage in three-dimensional gravity driven flow. Sample calculations with applications to glass melting furnaces are presented. First, a consistent set of thermophysical properties of the most common composition (74SiO₂-16Na₂O-10CaO (mol%)) of soda-lime silicate glass or similar compositions over the temperature range of 1000-2000 K is reported. The population balance equation is solved for the bubble density function using the backward method of characteristics. The zeroth to third order moments, i.e., number of bubbles, average radius, molar gas fraction, interfacial area, and void fraction are computed by numerical integration. Results for both transient and steady state operations are presented and analysed. Two cases are considered (1) bubbles containing only CO₂ and (2) bubbles containing a diffusing gas (O₂) and a non-diffusing gas (CO₂). The feasibility of such complex calculation is demonstrated and is in qualitative agreement with reported results.     

Liquid phase epitaxial growth of Ca,Ge-Substituted garnet films having magnetic bubbles 1.0–3.0 μm in diameter

Ca, Ge-substituted, magnetic garnet films which would support bubbles of 1.0–3.0 μm diameter were grown by isothermal deposition frm supersaturated PbO-B₂O₃ fluxes upon garnet films were yttriumm iron garnet Y₃Fe₅O₁₂, in which rare earths substituted for yttrium and Ge substituted for Fe. Ca was added to charge compensate the Ge. A typical composition of a 2 μm bubble film might be Y_{1.35Lu0.3Sm0.6Ca0.75Fe4.25O12}, but the compositions of the films were varied by modifying the composition of the growth solution and the growth conditions. The magnetic properties of the films were dependent upon film perfection and composition. Bubble mobilities ranged ≈300–1000 cm/sec-Oe. The films, whose thickness varied from 1.0–3.0 μm to match buble diameters, were uniform in thickness to less than 0.30 μm across a 2.54 cm diameter slice. The properties of the films were sufficiently stable with temperature from 0–100°C to indicate that these materials could be used in memory devices.     

The influence of ambient gas atmosphere on the liquid and solid composition at liquid phase epitaxial growth of GaAs–Alx-Ga1−xAs layers

Epitaxial gallium arsenide and gallium aluminium arsenide layers were grown from gallium solution on chromium-doped semi-insulating gallium arsenide. The effect of residual water concentration in the ambient gas atmosphere on change of aluminium in Al_xGa_1−xAs was determined. It was shown that a water concentration less than 5 ppm is necessary to grow epitaxial layers with high reproducible XAlAs-content and low carrier concentration.     

Hydride-assisted growth of GaN nanowires on Au/Si(0 0 1) via the reaction of Ga with NH3 and H2

High quality, straight GaN nanowires (NWs) with diameters of 50 nm and lengths up to 3 μm have been grown on Si(0 0 1) using Au as a catalyst and the direct reaction of Ga with NH₃ and N₂:H₂ at 900 °C. These exhibited intense, near band edge photoluminescence at 3.42 eV in comparison to GaN NWs with non-uniform diameters obtained under a flow of Ar:NH₃, which showed much weaker band edge emission due to strong non-radiative recombination. A significantly higher yield of β-Ga₂O₃ NWs with diameters of ≤50 nm and lengths up to 10 μm were obtained, however, via the reaction of Ga with residual O₂ under a flow of Ar alone. The growth of GaN NWs depends critically on the temperature, pressure and flows in decreasing order of importance but also the availability of reactive species of Ga and N. A growth mechanism is proposed whereby H₂ dissociates on the Au nanoparticles and reacts with Ga giving Ga_xH_y thereby promoting one-dimensional (1D) growth via its reaction with dissociated NH₃ near or at the top of the GaN NWs while suppressing at the same time the formation of an underlying amorphous layer. The higher yield and longer β-Ga₂O₃ NWs grow by the vapor liquid solid mechanism that occurs much more efficiently than nitridation.